SYNTAX: one of the constraints on movement proposed by Ross (1967). It states that

No element dominated by an S may be moved
out of that S if that S is dominated by
an NP which itself is immediately
dominated by S,

and is meant to capture the fact that categories cannot be moved out of a sentential subject.
EXAMPLE: consider (i) and (ii), both containing a sentential subject
(the for-clause and the that-clause respectively).